Respirators and other masks for supplying breathing gas to the user typically have facepieces made of a soft compliant material, such as rubber to form a seal with the user's face. In order to support filters and exhalation valves and the like, some masks have been made so that the rubber is thick, which undesirably makes the mask heavy and uncomfortable to wear, as well as more expensive to manufacture. However, if the rubber thickness is reduced, the mask may tend to collapse onto the user's face especially when the harness is tightened for donning the mask.
U.S. Pat. No. 5,062,421 describes a respirator mask wherein a large single rigid insert serves as a structural member for attachment of filter cartridges and an exhalation valve assembly and for support of the facepiece which is permanently sealed thereto. Each filter cartridge is described as asymmetric and swept back to shift the center of gravity inwardly toward the wearer's head, thus making the mask seem to be lighter to the wearer. This insert has swept-back cheek portions and is otherwise formed to conform to the shape of the mask, i.e., non-flat. Not only is such a mask not flexible enough to provide a comfortable fit over various face sizes but the non-flat insert is difficult to manufacture.
In order to provide a more comfortable fit, U.S. Pat. No. 5,592,937 discloses a respirator mask having a very soft compliant facepiece that has several stiffening elements integrated therein. The stiffening elements include an exhalation valve structure and structures for mounting filter cartridges, respectively. A yoke to which harness straps are attached is placed on top of the facepiece. Such a mask may be more flexible than desired due to the rubber material between the elements. Although the elements are flat, the requirement of more than one of them, as well as the requirement of the yoke, undesirably increases the manufacturing costs.
Accordingly, what is needed is a mask that is inexpensive to manufacture and that provides a comfortable sealing fit over various face sizes while having sufficient rigidity so that it does not collapse during normal use.